[Nexus 7 (2013) Q&A] hix3r:
Testing

Thank you for looking at it. All right, I backed up all the partitions from recovery just in case with adb pull /dev/block/mmcblk0p1-29 to img files, except the system and cache partitions.

Restock finished without any problems I restored the original partition layout (the only modification before was your non destructive system partition size increase that shrinks the cache partition).

I installed the APK with adb install from the PC and ran the test for 67 minutes from the battery, charger not plugged in. Temps got to 75-76C when the CPU started lowering the clocks from 1.52GHz to 1.13GHz. Zero reboots. I then left it alone for 9-10 hours on the charger, but zero reboots in idle too.

The only out of ordinary event was during the test: the battery indicator suddenly jumped to 4% from 83% gave a warning for low battery, then jumped back to 83%, there is a sudden dip in the battery charge log to 4% then back to the previous value, It happened 30 minutes into the test, but never repeated during the next 37 minutes, or the next 9-10 hours of idle. Something pulled the voltage down for a split second?

EDIT:

I saved the battery history with dumpsys batterystats, although it doesn't say what could have caused it: pastebin DOT com SLASH K58UCfqr

I re-ran the test on battery for 45 minutes and there were no battery drops or anyting this time, it seems to be unrelated to the CPU usage.

But the zero reboots for me is not surprising at all. The reboot problems were going on for years, I tried but never could reproduce it intentionally. There were some observations I made about them when they happened:

1. I never noticed the tablet reboot during heavy use, if I was watching HD movies, Youtube at 60FPS, playing a game, so during periods when the back of the tablet got warm I never got a reboot even if I used it for hours continously. Sometimes it would seem to freeze/slow down but it was processing and it would catch back up, didn't reboot.

2. The only time I remember annoying reboots during use were during very light load, example: I was reading a book from a PDF on the tablet, touched the screen to scroll lower and the tablet would freeze and reboot. Then I went back to read for 1-2 hours and again without issues could scroll the PDF fine etc., then again after some random amount of time when I tried to scroll at some random page it rebooted again.

3. I noticed the tablet rebooting during idle next to my desk on some days multiple times in a day, nothing was actively running on it, display was off, tablet idle, and you would notice the Google logo light up from the corner of your eye, and it rebooted again. I figured some background process/update started that triggered the reboot.

4. When I changed the battery I didn't notice any reboots for a couple days (could have still happened while I was sleeping) so I was hopeful a battery change fixed it. But after some time they started again. So I got the idea that maybe physically disconnecting the battery for a while would reset/fix something and tried that and it again didn't reboot for a couple days, but then it started again. But I only did this once so it could be I was just "lucky" with not getting reboots, I wouldn't rely on this observation. (Plus I can't be bothered to do this every couple of days as a "fix")

I actually went through 2 new batteries, after the original failed the first one was from AliExpress and it "worked" but was behaving weird. The charge indicator was always at 100% and when the battery drained it suddenly went to 0% and turned the tablet off. I installed AccuBattery and monitored the voltage from there because the actual voltage was slowly decreasing but the charge indicator was monitoring the wrong voltage or something. Capacity wise it was okay, lower than what was advertised but similar to the factory battery capacity.

I bought another one and this is working fine, charge indicator works, capacity is fine. But the reboots were present on the original/the AliExpress/and this current battery all the same.

All of this made me think of the flash storage as a culprit:

- scrolling a PDF required a read from disk, the chip gave back a read error, the kernel threw an exception and the tablet rebooted

- maybe the random idle reboots were again some background process trying to read the flash memory, read error, reboot

But it seems the eMMC chip is fine?

Another theory I have is that some SMD capacitors or a capacitor inside an IC is busted on the board and can't supply the charge required "sometimes" when the circuit suddenly does some work however the circuit is stable when the work is done continously, so I am not sure this can be narrowed down or possible even.

As the reboots seemingly are absolutely random during idle I couldn't reproduce them and pull some system logs either... As you can see it seems to work fine even during idle for days/hours "sometimes".